SASKATOON — Water volume trumps water use efficiency, says Phillip Harder, research director and hydrological scientist at Croptimistic Technology.
“The gains when it comes to improving water use efficiency on its own — that’s not what’s going to get you more production,” he said during Saskatchewan Agriculture’s crop water use efficiency webinar last month.
“What’s going to get you more production is just increasing the amount of crop available water.”
This is one of the basic principles of hydrology, which is Harder’s specialty.
He said the number one way to do that is to take better advantage of all forms of precipitation, including rainfall, spring runoff and winter snowpack. Changes in runoff, subsoil flow, water infiltration and snow retention all play into the increase of transpiration.
Harder said precipitation during the growing season makes up much less of crop water use than water stored in the soil in average and dry years. The only exception is wet years, when the levels are nearly equal — rarely does growing season precipitation exceed stored moisture.
“We often think, ‘oh, the ground froze. Nothing’s moving. Everything is static.’ And often, the conceptual model is, snow will just run off anyways, it doesn’t really matter. But it really does,” he said.
As soil freezes, warms and re-freezes, the freezing front moves deeper into the soil profile. Then, when snow melt occurs, snowpack reduces and soil thaws from the surface and from the soil depth. There isn’t a “capping” of the infiltration, as one may assume.
With these pieces in mind, there’s a few things to consider.
“There can be redistribution of water in our soil profile, just from this freezing front dropping through it,” Harder said.
“So, we can have movement of water closer to the root zone from that mechanism as well.”
However, this movement is dependant on soil conditions, such as if it’s dry or saturated when fall freeze up occurs.
He said mid-winter melts can indeed infiltrate subsoil during winter and that a lot of infiltration occurs with the end of season snow melt. As well, the depth of the snowpack determines the depth of the freezing front and melt timeline, influencing above and below the surface.
There are three categories of infiltration: unlimited, limited and restricted. The ideal is unlimited, when the soil in fall is dry, coarse and cracked at the time of freeze up, which makes it extremely permeable to water come spring melt.
Restricted is the worst case scenario, caused by soil that was well saturated from a late fall rain or long mid-winter melt event, which creates a “concrete frost saturated layer.”
The most common reality is a limited situation, which has a degree of soil saturation from fall but not enough to limit permeation from a mid-winter or spring melt.
“This year, we’ve got a ton of snow,” he said.
“Even if we have mid-winter melts, generally they’re not going to get to the point where they’re able to actually melt enough to percolate enough water through the snow to then refreeze because of all the insulation that we’ve got to deal with first.”
Last fall was dry, putting Saskatchewan in a limited – nearly unlimited – infiltration position. Paired with the current snow fall, it’s a hopeful situation. Even with likelihood of runoff, there is potential for strong infiltration.
Another key point is that snow has greater water density than may be believed.
“Snow has a ton of water, it’s not a one to 10 ratio. It’s not 10 per cent water out there. Because of snow metamorphosis, blowing around, all those factors, we can actually have quite an increase in snow density over the course of the winter.”
In a recent experiment near his home at Clavet, Sask., Harder found that the snow had 24 per cent water content, which is approximately 75 millimetres of water. That will increase as the snow melts and further infiltrates the snowpack before refreezing. He expects to see up to 40 per cent water content at final melt.
So, to take advantage of the snow, producers must manage blowing snow effectively. The best ways to do so are to use taller stubble as a snow trap and be mindful of ridging.
“Anything you can do to increase the roughness of your surface — basically stubble height — will increase the amount of snow that can be retained on the surface.”
In an average year, a centimetre of stubble is equivalent to a millimetre of water. Harder recommends a stubble height of 30 centimetres, saying it’s a “safe height.”
While even higher stubble would be beneficial in years with greater snow fall, it’s hard to predict nature.
Regional variability must also be considered. Northern areas accustomed to more snow would see a greater benefit by exceeding the 30 cm height, while the southern, drier areas likely wouldn’t gain much by going higher.
There hasn’t been significant data on ridging since the 1980s, but it can be a helpful practice for creating surface roughness. However, Harder warns to consider winter conditions and weather patterns, saying it has potential to reduce soil infiltration capacity.
“After you plowed the snow, did you get more snow right away, or did you have a warm period and have some melts that refroze in that surface?… Yes, you’re getting more snow in that particular location, but it may have to run a ways before it can infiltrate into an area where there is retained snow that has been insulating (the surface).”
Ridging is best done during cold periods when more snow is expected soon to ensure good insulation and snow catch.
For moisture retention, crop residue is the way to go. However, a balance has to be found between stubble height and enough residue to catch snow and limit evaporation.
“Stubble is really good for maximizing the amount of water in your landscape, residues are really for maximizing retention of whatever water has made its way into your surfaces. You’re always going to have some soil evaporation, but residues can really tamp it down — a lot.”
In a study on the impact of surface and residue management on water availability, Harder found that nearly 20 per cent of a year’s production can be affected by surface and residue management techniques.
If a producer is trying to decide on increasing stubble height or prioritizing residue, consider your region, typical weather conditions, equipment and crop rotations. Each factor plays a part, Harder said.
“It depends where you’re at. There’s no good answer.”
About the author
Related Coverage
Wetland advocates hoped Sask. election would talk water
Old water management concept continues to work
Network promotes better farm drainage communication
Landowners struggle with unapproved drainage
Critical Ground highlights the need for research during Canada’s Outdoor Farm Show
